As shown schematically in FIG. 1, an analog-digital converter with a pipeline architecture DCANPA comprises several stages (in this instance N stages), each of which usually has a fairly low resolution (from 1 to 3 bits in general). The first stage receives an analog signal SAE and the converter DCANPA delivers at the output a corresponding digital word MNS. Each of the stages has a sample-and-hold (sample-and-hold) S/H in order to sample the signal originating from the previous stage, a signal commonly referred to by those skilled in the art as the “residue.”
Each stage moreover comprises an analog-digital conversion circuit CAN delivering b bits and followed by a digital-analog conversion circuit. The output of the digital-analog converter CNA is subtracted from the signal originating from the sample-and-hold S/H and then amplified in an amplifier AMP with a fixed gain g.
The b bits of each stage undergo digital correction in a block BCR to form the output digital word MNS. This type of pipeline-architecture converter notably has the advantage of having a sampling speed that is independent of the number of stages used and a good tolerance with respect to the offsets of the comparators of the circuits CAN.
In data-conversion systems, this type of analog-digital converter is usually associated with a programmable gain amplifier PGA, placed in front of the input of the analog-digital converter, which makes it possible to adjust the amplitude of the input analog signal, voltage Vin, for example, as illustrated in FIG. 2. The programmable gain amplifier PGA is, for example, controlled by automatic gain control means or a typical automatic gain controller AGC.
A potential drawback of such an implementation lies in the fact that the programmable gain amplifier PGA may be designed to introduce negligible noise and negligible distortion into the signal. Otherwise, the analog-digital conversion carried out in the converter DCANPA may contain an error. In addition, for example, in continuous-time systems based on resistance ratios, the noise is a function of the value of the resistance. Consequently, the resistance value may be reduced to obtain a lower noise, which involves a great increase in power consumption.